Metal extrusion



April 29,1958 G. P. KRAUSE 2,832,468

METAL EXTRUSION Filed Sept. 14, 1954 METAL EXTRUSION Gerhard P. Kranse, Harrison, N. Y., assignor, by mesne assignments, to llaldwin-Lima-Harnilton Corporation, Philadelphia, Pin, a corporation of Pennsylvania Application September 14, 1954, Serial No. 455,848

1 Claim. (Cl. 207-9) the quality of the extrusion and, in addition, causes rapid wear of the costly dies due to the abrasive or scouring effect of the chilled parts and hard scale particles. If chilled or oxidized particles from the outer surface of the billet flow along the die, they tend to .tear further particles loose from the front face of the billet chilled by contact with the die.

Various attempts have beenmade to overcome these difficulties, as, for instance, by leaving a large butt end wherein scale accumulates, or by breaking the scale prior to its entry into tne die. Another proposed solution consists in providing special lubricants of glass and salt bath material to protect the dies. All of these measures have failed to solve the problem fully. The formation of scale may be reduced by using an inert atmosphere or immersing the billets in a salt bath furnace, but these steps are costly and cumbersome and do not fully meet all requirements.

In the extrusion of certain metals it is common to use a dummy block or pressing disk of a diameter smaller than the internal diameter of the container so that the outer layer of the billet will not be extruded but rather left in the container as a shell or sleeve. Thus the chilled outer skin of the billet normally containing a substantial amount of scale is retained in the press until the extrusion is completed. However, the thickness of skin which is thus retained has been very limited since the gap between the pressing disk and the container must be small enough to provide sufficient friction to prevent back extrusion (escape of metal from the container in a direction opposite to the direction of movement of the stem). Such limited thickness of skin is in many cases insufficient to remove the oxidized, chilled layer which may extend to greater depths. In the case of metals such as steel, back extrusion may occur regardless of the thickness of the skin since the metal shows little adherence to the wall of the container.

It is therefore an object of this invention to provide a method and means whereby the oxidized and chilled circumferential layer of a billet may be separated from the metal to be extruded, without causing back extrusion and without forcing any detrimental amount of the oxidized and chilled material through the die, even Where the layer is relatively thick or the metal shows little adherence to the wall of the container.

As stated hereinbefore, the billet is oxidized and chilled not only on the surface which engages the con- 2,832,468 Patented Apr. 29, 1958 tainer wall but also at its end where it engages the die assembly. It is therefore a further object of this invention to provide a method and means for preventing extrusion of a detrimental amount of oxidized and chilled material from the end of the billet through the opening in the die assembly.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

The accompanying drawing is a longitudinal section through the container and asociated parts of an extrusion press.

Referring to the drawing, there are shown those parts of an extrusion press to which this invention is applied. A. container 10 is provided with a bore through the loading or back end of which the preheated billet is moved into extruding position. At its discharge or front end the container is provided with a die assembly comprising a die holder 12; in which is supported the die 15, and die backer 16. The discharge end of the container is thus closed except for the passageway 17 through the die assembly through which the metal is to be extruded by a dummy or pressure disk 20 and a stem 21 to which pressure is applied from a suitable source (not shown).

As stated hereinbefore, it has been common practice in the extrusion of certain metals to make the diameter of the dummy or pressing disk 20 slightly smaller than the interior diameter of the container in order to leave behind a sleeve formed by the outer skin of the billet. This skin, however, was limited to a relatively small thickness so that frictional resistance to ilow of metal through the passageway would be sufiiciently high to prevent back extrusion. A skin of such relatively small thickness is often insufficient to remove the entire depth of oxidized and chilled material, particularly in the case of certain high temperature, high strength metals such as carbon steel, alloy steel and titanium. Therefore, I provide a relatively large gap 40 between the pressing disk and the inner wall of the container, sufficient to detach and leave behind the entire depth of oxidized and chilled material where such depth is relatively large so that the frictional resistance to flow of metal in the passageway between disk and container would be insufiicient alone to prevent back extrusion. For this reason, i provide a closure plate 25 for closing the back opening or loading end of the container, except for an opening 26 through which the stem operates. This will effectively prevent back extrusion no matter how large the depth of skin to be removed. Plate 25 is held in operative position by suitable means (not shown), and may be removed when the billet and pressing disk 20 are to be inserted into the container. To facilitate the operation, the plate 25 may be of split construction. The inner limit of the skin which will be separated from the billet is indicated at 41.

The above arrangement will cause to be left behind in the form of a sleeve or shell within the container the oxidized and chilled outer layer of the billet which engages the wall of the container. However, the end of the billet which engages the die assembly also has a layer of oxidized and chilled material which if forced through the die would seriously damage the die and impair the quality of the extrusion. To obviate this deleterious effect, I have provided means for entrapping this skin material so that it cannot reach the die opening. For this purpose the inner surface of the die assembly is inclined in the direction of extrusion from a region El) closely adjacent the die opening 17 outwardly toward the container wall. This forms a. circumferential pocket 513 which will effectively trap and immobilize the oxidized and chilled end layer because in order to reach the die opening it would have to move in a direction opposite to the direction of the extrusion pressure. The forward, extrusion movement of the stem is stopped in a plane such as P while there is an appreciable portion of billet left behind, such portion including entrapped oxidized and chilled material.

In the case of metal such as steel which shows little adherence to the wall of the container, the use of the closure plate 25 will be of advantage even when the thickness of the skin is small. In the case of high strength light metal alloys, the closure plate may be used for obtaining a relatively thick shell.

If desired, the stem may have a bore therethrough in the conventional manner to accommodate a mandrel. the extrusion of tubular material. The hereinbefcje described invention which prolongs the life or" the die by immobilizing oxidized and chilled material will benefit the mandrel for the same reasons.

Having described my invention, what li claim and desire to secure by Letters iatent is:

In an extrusion press comprising a container having a passage therethrough for receiving a preheated metal billet, a die assembly including a die having an opening therethrough, said assembly being adapted to close one end of the container except for said die opening, a stern, and a pressing disk disposed to be engaged by the stem, said stern and disk being adapted to enter the other end of the container and be moved under pressure against the billet so as to force the metal through the die opening, the circumference and ends of the billet being subject to the formation of oxide thereon and to chilling, the improvement which consists in means for preventing the passage of a detrimental amount of oxidized and chilled portions of the billet through the die opening, said means comprising said pressing disk having a contour smaller than the inner contour of the container wall by an amount substantially equal to the thickness of the oxidized and chilled circumferential portion of the billet, whereby the movement of the stem in the direction of extrusion will leave behind said oxidized and chilled circumferential portion of the billet as a sleeve within the container wall, and a closure member having an opening through which said stem operates and adapted to close said other end of the container when the stem operates in said opening of the closure member, the face of the die nearer the billet being inclined in the direction of extrusion from a region adjacent the die opening so as to form a pocket between the die assembly and the container wall to hold the chilled and oxidized material at the end of the billet contacting the die.

References Cited in the file of this patent UNITED STATES PATENTS 436,929 Wallace Sept. 23, 1890 1,955,243 Liebergeld et al Apr. 17, 1934 2,165,711 Kreidler luly 11, 1939 2,688,400 Ansel Sept. 7, 1954 2,738,064 Kreidler Mar. 13, 1956 2,753,044 Haendeler July 3, 1956 FOREIGN PATENTS 271,378 Germany Mar. 11, 1914 546,446 Great Britain July 14, 1942 607,285 Great Britain Aug. 27, 1948 715,411 Germany Dec. 20, 1941 1,057,678 France Mar. 10, 1954 

